For each cylinder, place the cam lobe pointing up. Slide your index finger between the bottom of the rocker and the ridge of the ball stud. Mentally note the gap - like 4 mm. Now rotate the cam lobe down. Feel the gap. If it changed more than "a little bit," the HLC is weak.

After you have done a few, you get a better feeling for what the gap should be.

Note that if the rocker is down - like only a 1 mm gap - with the cam tip up, it is collapsed.